X1 2 3 4 5 y 3 6 9 12 15 given the table, write an expression for the function, and describe what it does. a) y = 2x. y is double x. b) y = 3x. y is triple x. c) y = 2x+1. y is twice x plus 1. d) y = 2x-1. y is twice x minus 1.